Nanofiber Material Promises Better Li-ion Batteries

It looks like a roll of duct tape, but it is very sophisticated stuff that promises to significantly improve the performance and safety of lithium-ion batteries.

Shown off for the first time at a recent automotive conference, it is a nanofiber-based polymeric battery separator DuPont Co. says can increase battery power 15% to 20%, increase battery life up to 20% and improve battery safety by providing thermal stability at high temperatures.

Michael Sanders, global business director-DuPont Energy Storage Solutions, says about 20 companies are evaluating the material for second-generation Li-ion battery designs, including battery manufacturers, auto makers and Tier 1 suppliers.

Part of a $50 million development effort, DuPont has been manufacturing initial quantities of the separator material at sites in Seoul and Wilmington, DE.

But a new U.S. plant in Chesterfield County, VA, is under construction and will be completed in first-quarter 2011. It will be ready for regular production in the following quarter, Sanders says.

Tapping the yellow, duct tape-like roll next to his lunch plate during an interview, Sanders says the separator film, dubbed “Energain,” is the product of DuPont expertise in nanoscience, chemical engineering, fiber sciences, polymer synthesis, polymer modification and applications development.

A typical laptop computer might have six individual Li-ion cells, but hybrid-electric vehicles contain between 50 and 70. Plug-in electric vehicles with range-extending motors have from 80 to more than 200 such cells and an all-electric vehicle might carry 150 or more.

Within each battery is a separator sheet positioned between two electrodes. The barrier prevents the electrodes from touching and shorting while letting lithium ions pass back and forth to allow the charge and discharge of the battery.

The DuPont separator material is produced with a proprietary spinning process that creates continuous nanofiber filaments that give the material special qualities. For instance, they do not shrink in high temperatures and are easily saturated with electrolyte liquids during battery manufacture.